docs: def fetch_archive(savedir, url, fname, force=False):
      """download an archive to a specific location"""
      dest = pjoin(savedir, fname)
      if os.path.exists(dest) and not force:
          info("already have %s" % fname)
          return dest
      info("fetching %s into %s" % (url, savedir))
      if not os.path.exists(savedir):
          os.makedirs(savedir)
      req = urlopen(url)
      with open(dest, 'wb') as f:
          f.write(req.read())
      return dest